U.S. patent application number 11/418306 was filed with the patent office on 2006-11-09 for poly (vinyl alcohol) - based formaldehyde-free curable aqueous composition.
This patent application is currently assigned to Dynea Austria GmbH. Invention is credited to Elena Pisanova, Robert Schmidt, Alexander Tseitlin.
Application Number | 20060252855 11/418306 |
Document ID | / |
Family ID | 37396228 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060252855 |
Kind Code |
A1 |
Pisanova; Elena ; et
al. |
November 9, 2006 |
Poly (vinyl alcohol) - based formaldehyde-free curable aqueous
composition
Abstract
A formaldehyde-free curable aqueous composition containing
polyvinyl alcohol, a multi-functional crosslinking agent, and,
optionally, a catalyst. The composition may be used as a binder for
non-woven products such as fiberglass insulation. The non-woven
products are formed by contacting the formaldehyde-free curable
aqueous composition with fibrous components and the mixture is
cured to form a rigid thermoset polymer providing excellent
strength and water resistance of the cured nonwoven product.
Inventors: |
Pisanova; Elena;
(Mississauga, CA) ; Schmidt; Robert; (Thornhill,
CA) ; Tseitlin; Alexander; (Mississauga, CA) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Dynea Austria GmbH
Krems
AT
|
Family ID: |
37396228 |
Appl. No.: |
11/418306 |
Filed: |
May 5, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60678229 |
May 6, 2005 |
|
|
|
Current U.S.
Class: |
524/47 |
Current CPC
Class: |
C08K 5/04 20130101; D21H
17/06 20130101; D21H 17/36 20130101; C08K 5/07 20130101; C08K 5/04
20130101; C08K 5/07 20130101; C08L 29/04 20130101; D21H 17/15
20130101; C08K 5/092 20130101; C08L 29/04 20130101; C08L 29/04
20130101; C08L 29/14 20130101; C08K 5/092 20130101; C08L 2666/26
20130101; D04H 1/587 20130101; D21H 17/28 20130101; D04H 1/64
20130101; D21H 13/40 20130101; D21H 25/06 20130101; C08L 29/04
20130101; C08L 3/00 20130101 |
Class at
Publication: |
524/047 |
International
Class: |
D21H 19/54 20060101
D21H019/54 |
Claims
1) A curable aqueous composition prepared by a process comprising
combining the following components: (a) a hydroxy-containing
polymer; (b) a multi-functional crosslinking agent which is at
least one selected from the group consisting of a nonpolymeric
polyacid, salts thereof, an anhydride, and a nonpolymeric
polyaldehyde, and optionally (c) a catalyst; wherein the weight
ratio of (a):(b) is from 95:5 to about 35:65, wherein the curable
composition has a pH of at least 1.25.
2) The curable aqueous composition of claim 1, having a pH in the
range of about 2.5 to about 6.5.
3) The curable aqueous composition of claim 1, wherein when the
multi-functional crosslinking agent is at least one selected from
the group consisting of a nonpolymeric polyacid, salts thereof and
an anhydride then the pH of the curable aqueous composition is
adjusted to be in the range of 3.0-4.0.
4) The curable aqueous composition of claim 1, wherein the
hydroxy-containing polymer is polyvinyl alcohol having a number
average molecular weight in the range of greater than 7,000.
5) The curable aqueous composition of claim 4, wherein the
polyvinyl alcohol has a number average molecular weight in the
range of 12,000 to 85,000.
6) The curable aqueous composition of claim 4, wherein the
polyvinyl alcohol has a number average molecular weight in the
range of greater than 13,000 to 45,000.
7) The curable aqueous composition of claim 1, having a nonvolatile
content greater than 30 wt %.
8) The curable aqueous composition of claim 1, having a nonvolatile
content of 32-43 wt %.
9) The curable aqueous composition of claim 1, wherein said
hydroxy-containing polymer is a combination of polyvinyl alcohol
and at least one selected from the group consisting of starch,
modified starch and a sugar.
10) The curable aqueous composition of claim 1, wherein said
hydroxy-containing polymer is a combination of polyvinyl alcohol
and starch.
11) The curable aqueous composition of claim 10, wherein the
polyvinyl alcohol is formed by hydrolyzing polyvinyl acetate or a
copolymer of ethenol and vinyl acetate, wherein the final polymer
is 70 mole % to 99 mole % hydrolyzed.
12) The curable aqueous composition of claim 1, wherein said
hydroxy-containing polymer has a viscosity up to 10 centipoise when
in a 4% aqueous solution at 20.degree. C.
13) The curable aqueous composition of claim 1, wherein the
multi-functional crosslinking agent is a blocked nonpolymeric
polyaldehyde.
14) The curable aqueous composition of claim 13, wherein the
nonpolymeric polyaldehyde is blocked with a blocking agent which is
at least one selected from the group consisting of urea, ethylene
urea, sorbitol, and ethylene glycol.
15) A cured composition comprising a nonwoven fiber in a cured
binder wherein the cured composition is formed in a process
comprising combining nonwoven fibers with the curable aqueous
composition of claim 1 to form a mixture and curing the
mixture.
16) The cured composition according to claim 15, wherein the
process includes a step of diluting the curable aqueous composition
with sufficient water so the curable aqueous composition has 5% by
weight of nonvolatiles prior to the curing step.
17) The cured composition according to claim 15, wherein the
nonwoven fiber is fiberglass.
18) A method of forming a curable aqueous composition comprising
the following steps: a step of combining (a) a hydroxy-containing
polymer with (b) a multi-functional crosslinking agent which is at
least one selected from the group consisting of a nonpolymeric
polyacid, salts thereof, an anhydride, and a nonpolymeric
polyaldehyde, and optionally (c) a catalyst to form a curable
aqueous composition; and with the proviso that if the curable
aqueous composition has a pH of below 1.25, then the method further
comprises a step of adding sufficient base to raise the pH to at
least 1.25; and wherein the weight ratio of (a):(b) is from 95:5 to
about 35:65.
19) The method according to claim 18, wherein the multifunctional
crosslinking agent is a blocked nonpolymeric polyaldehyde or an
anhydride.
20) The method according to claim 18, wherein the
hydroxy-containing polymer is polyvinyl alcohol having a number
average molecular weight in the range of greater than 7,000.
21) The method according to claim 18, wherein the multi-functional
crosslinking agent is at least one selected from the group
consisting of a nonpolymeric polyacid, salts thereof and an
anhydride and sufficient base is added to raise the pH to be in the
range of 3.0-4.0.
22) A method for forming a nonwoven material comprising the
following steps: combining (a) a hydroxy-containing polymer with
(b) a multi-functional crosslinking agent which is at least one
selected from the group consisting of a nonpolymeric polyacid,
salts thereof, an anhydride, and a nonpolymeric polyaldehyde, and
optionally (c) a catalyst to form a curable aqueous composition;
and with the proviso that if the curable aqueous composition has a
pH of below 1.25, then the method further comprises a step of
adding sufficient base to raise the pH to at least 1.25; and
combining the curable aqueous composition with nonwoven fiber, and
heating the curable aqueous composition and nonwoven fiber at
130.degree. C. to 250.degree. C. for sufficient time to effect
cure, wherein the weight ratio of (a):(b) is from 95:5 to about
35:65.
23) The method for preparing the nonwoven material of claim 22,
further comprising a step of diluting the curable aqueous
composition with sufficient water so the curable aqueous
composition has 95% by weight of water prior to the heating
step.
24) The method for preparing the nonwoven material of claim 22,
wherein the nonwoven fiber is fiberglass.
25) The method for preparing the nonwoven material of claim 22,
wherein the multi-functional crosslinking agent is at least one
selected from the group consisting of a nonpolymeric polyacid,
salts thereof and an anhydride and sufficient base is added to
raise the pH to be in the range of 3.0-4.0.
Description
[0001] This Nonprovisional application claims priority under 35
U.S.C. .sctn. 119(e) on U.S. Provisional Application No. 60/678,229
filed on May 6, 2005, the entire contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to thermosetting self-crosslinking
formaldehyde-free resins, a process for preparing said resins and
their use as binders for nonwovens.
BACKGROUND OF THE INVENTION
[0003] Formaldehyde-based resins, e.g. Phenol-Formaldehyde (PF),
Melamine-Formaldehyde (MF), Urea-Formaldehyde (UF) resins are
widely used as nonwovens binder for various industrial applications
such as fiberglass insulation industry, paper impregnation,
filtration media, and roofing materials. These formaldehyde-based
resins are inexpensive, have low viscosity, and are able to cure to
form a rigid polymer, thereby providing the finished product with
excellent physical properties.
[0004] Fiberglass insulation products consist of glass fibers
bonded together with covalently crosslinked binder resins.
Processes for making fiberglass insulation generally include
drawing molten streams of glass to spinning wheels where they are
spun into thin fibers by centrifugal force. The fibers are then
blown into a forming chamber, sprayed with an aqueous binder and
deposited as a mat onto a traveling conveyor. Thereafter, the
coated mat is transferred to a curing oven where heated air is
blown through the mat to cure the binder and rigidly bond the glass
fibers together.
[0005] PF resins, typically extended with urea, are widely used
throughout the fiberglass insulation industry.
[0006] PF resins are also used as a binder for nonwoven filtration
media. These filtration products are typically made by a wet-laid
technique wherein fibers, e.g. glass or cellulose fibers, are
dispersed in aqueous binder slurry. The fibers are then deposited
from the binder slurry onto a conventional screen or wire as in a
Fourdrinier machine to form a mat, which includes a binder resin,
e.g., a phenolic resin.
[0007] MF resins are used in manufacturing overlay paper laminates.
In general, a porous substrate, such as paper or a fabric web, is
impregnated with an MF resin and dried. The dried resin impregnated
substrate, along with other layers, are pressed usually with heat
to form a laminate.
[0008] Glass fiber mats for roofing industry are made by applying a
UF-based binder to a wet glass fiber mat, followed by drying and
curing the binder at elevated temperatures.
[0009] A serious disadvantage of PF, MF and UF resins is high
concentration of free formaldehyde, which is undesirable for
ecological reasons. During the curing reaction, formaldehyde is
volatilized from the binder into the surrounding environment.
Although addition of urea to PF resins results in decreasing
formaldehyde emissions, at the same time, ammonia emissions and
"blue smoke" increase dramatically. Therefore, there is a
continuing need for alternative nonwovens binder that would not
emit formaldehyde upon curing.
[0010] A number of formaldehyde-free compositions have been
developed for use as a binder for making nonwoven products.
[0011] U.S. Pat. No. 4,076,917 discloses the use of
beta-hydroxyalkylamides to cure polycarboxy polymers such as
polyacrylic acid. Such a system, however, is too viscous for use as
a fibrous glass binder.
[0012] U.S. Pat. No. 5,143,582 discloses heat-resistant nonwovens
containing ammonia-neutralized polycarboxylic acids, either
monomeric or polymeric, and beta-hydroxyalkylamides.
[0013] However, the binder compositions are believed to liberate
ammonia upon cure. Ammonia emissions are becoming increasingly
tightly regulated.
[0014] U.S. Pat. Nos. 6,221,973 and 6,331,350 describe a
formaldehyde-free fiberglass binder including a polyacid, such as
polyacrylic acid, and a polyol, with a molecular weight less than
about 1000, such as, for example, glycerol, triethanolamine,
sorbitol, or ethylene glycol. A phosphorous catalyst is used to
accelerate the cure of the composition.
[0015] U.S. Pat. No. 5,932,689 describes a curable aqueous
composition for fiberglass insulation, which contains (a) a
polyacid comprising at least two carboxylic acid groups, anhydride
groups, or salts thereof; (b) an active hydrogen-containing
compound, such as polyol or polyamine, and (c) a cyanamide, a
dicyanamide or a cyanoguanidine. Suitable accelerators include
phosphorous or fluoroborate salts.
[0016] WO 03/104284 describes an epoxide-type formaldehyde-free
insulation binder containing a substantially infinitely
water-dilutable or water-dispersable mixture of an epoxide and a
multi-functional cross-linker, such as polyamidoamine polymer.
[0017] Despite these disclosures, there is a growing need for new
formaldehyde-free aqueous compositions suitable for use as a binder
for fiberglass insulation, roofing and filtration materials, as
well as for paper impregnation.
[0018] Some of the drawbacks and limitations of the above-described
systems include high cost, high viscosity, low pH causing corrosion
of metal parts along the production lines, and high cure
temperatures. Thus, new formaldehyde-free binders having lower cost
and curing energy requirements similar to those of
phenol-formaldehyde resins are desired.
[0019] Polyvinyl Alcohol (PVOH) is a water-soluble polymer known to
have various uses in view of its excellent properties. PVOH is a
polymer with high tensile strength, excellent flexibility, good
water resistance and outstanding binding capacity (Finch, C. A.,
Ed., "Polyvinyl Alcohol: Properties and Applications", John Wiley
& Sons, 1973, pp. 227-230). In view of these advantageous
properties, PVOH has been used in the paper processing industry for
surface and internal sizing of paper and to impart water resistance
to paper. PVOH-based aqueous compositions are also used as coating
solutions. However, such systems are generally too viscous for use
as a fibrous glass binder.
[0020] U.S. Pat. Application No. 20030008586 discloses the use of
PVOH as a formaldehyde-free binder solution for low binder nonwoven
fiber mat useful for making wood product laminates. The binder
produces high bonding strength with wood and is characterized by
good storage stability. The binder is used at 5% concentration.
[0021] U.S. Pat. No. 6,444,750 describes a curable aqueous
PVOH-based coating solution for polymeric substrates. Organic acids
such as lactic acid, maleic acid, and citric acid are used as
cross-linking promoters. The pH of the solutions is 3.5 or less,
which provides substantially 100% cure of PVOH upon drying. The
coating solutions exhibit improved viscosity stability. However,
formaldehyde-containing crosslinkers are used as the crosslinking
agent.
[0022] U.S. Pat. No. 6,379,499 describes an aqueous composition for
paper treatment, which contains PVOH, a multifunctional aldehyde
and a catalyst. Glutaraldehyde and glyoxal are used as
cross-linking agent at a concentration of about 50% to about 800%
of the weight of PVOH. The aqueous compositions for paper treatment
contained about 1% PVOH. After curing the compositions at a
temperature between 100.degree. C. and 200.degree. C. for 0.5-5
minutes, the paper demonstrated improved tensile strength and
folding endurance.
[0023] U.S. Pat. No. 5,354,803 describes a nonwoven binder
containing a graft-copolymer of low or ultra-low molecular weight
PVOH (12-35%) and a vinyl and/or acrylic monomer (65-88%). The
binder is used as a latex (emulsion), which is applied to nonwoven
polyester roofing mat. After curing the compositions at a
temperature 149-154.degree. C. for 3-5 minutes, the nonwoven
products exhibit high temperature resistance, tensile strength and
elongation resistance.
[0024] U.S. Pat. No. 6,884,849 (hereinafter "the '849 patent")
describes a poly alcohol-based binder composition comprising a low
molecular weight polycarboxylic acid and a low molecular weight
poly-alcohol, such as PVOH having a number average molecular weight
of <7,000. The binder solution preferably comprises at least one
cure catalyst or accelerator, such as sodium hypophosphite. The
binder exhibits a high cure rate and provides a good recovery of
the final nonwoven product. However, a practical use of such a
composition for insulation production is limited by its rather low
concentration (10-30%) and the high acidity causes corrosion of
production lines and problems with cure strength of the final
binder product.
[0025] While these references and other prior art systems disclose
various PVOH-based curable compositions, they have certain
limitations with respect to developing a nonwoven binder. A number
of these systems have the disadvantage of using formaldehyde-based
cross-linkers. Other cross-linking agents release formaldehyde
during the cure, for example, N-methylol acrylamide. Further, these
conventional systems are used as diluted binders containing, as a
rule, 1-5% PVOH. This limitation is due to the high viscosity of
aqueous PVOH solutions.
[0026] Thus, there is a need in developing new PVOH-based nonwoven
binders that could be cured by non-formaldehyde cross-linkers. It
is desirable that such curable PVOH compositions contain higher
amounts of non-volatiles (sometimes referred to as "NV"
hereinafter) (about 25-40% by weight of the resin), and at the same
time are stable and infinetely water-dilutable.
SUMMARY OF THE INVENTION
[0027] The invention is drawn to a curable aqueous composition
comprising: (a) a hydroxy-containing polymer; (b) a
multi-functional crosslinking agent which is at least one selected
from the group consisting of a nonpolymeric polyacid, salts
thereof, an anhydride, and a nonpolymeric polyaldehyde, and
optionally (c) a catalyst; wherein the weight ratio of (a):(b) is
from 95:5 to about 35:65, and wherein the curable composition has a
pH of at least 1.25.
[0028] The invention is also drawn to a method for forming a
curable aqueous composition comprising: a step of combining (a) a
hydroxy-containing polymer with (b) a multi-functional crosslinking
agent which is at least one selected from the group consisting of a
nonpolymeric polyacid, salts thereof, an anhydride, and a
nonpolymeric polyaldehyde at a weight ratio of (a):(b) of from 95:5
to about 35:65, and optionally (c) a catalyst to form a curable
aqueous composition; and if the curable aqueous composition has a
pH of below 1.25, then the method further comprises a step of
adding sufficient base to raise the pH to at least 1.25.
[0029] The invention is also drawn to a cured composition
comprising a nonwoven fiber in a cured binder wherein the cured
composition is formed by combining the nonwoven fibers with said
curable aqueous composition to form a mixture and curing the
mixture.
[0030] The invention is also drawn to a method for forming a
non-woven material comprising: combining the nonwoven fibers with
said curable aqueous composition, and heating the mixture at
130.degree. C. to 230.degree. C. for sufficient time to effect
cure.
[0031] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0032] An embodiment of the invention is a curable aqueous
composition comprising: (a) a hydroxy-containing polymer; (b) a
multi-functional crosslinking agent which is at least one selected
from the group consisting of a nonpolymeric polyacid, salts
thereof, an anhydride, and a nonpolymeric polyaldehyde, and
optionally (c) a catalyst; wherein the weight ratio of (a):(b) is
from 95:5 to about 35:65, and wherein the curable composition has a
pH of at least 1.25. Preferably, the weight ratio of (a):(b) is
from 80:20 to 45:55, and most preferably, the weight ratio of
(a):(b) is from 65:35 to 50:50.
[0033] In an embodiment of the invention, the formaldehyde-free
curable aqueous composition of this invention may optionally be
neutralized with a base. In particular, the pH is adjusted with at
least one base selected from the group consisting of a nitrogenous
base, sodium hydroxide, and potassium hydroxide. It is preferred to
use a nitrogenous base and it is especially preferred that the
nitrogenous base is ammonium hydroxide or triethanolamine. The
preferred pH for the curable aqueous composition is up to 6.0. More
preferably, the pH for the curable aqueous composition is from
about 2.5 to 6.5. Even more preferably, the range of pH is 3.5 to
5.0. It is most preferred that the pH depends upon the type of
multi-functional crosslinking agent used, i.e., when the
multi-functional crosslinking agent is at least one selected from
the group consisting of a nonpolymeric polyacid, salts thereof, an
anhydride then the pH of the curable aqueous composition is in the
range of 3.0-4.0 and when the multi-functional crosslinking agent
is a nonpolymeric polyaldehyde, then the pH is greater than 4.0 up
to and including 6.5.
[0034] In an embodiment of the invention, (a) a hydroxy-containing
polymer is a polyvinyl alcohol (PVOH). However, it is envisioned
that the hydroxy-containing polymer is a combination of polyvinyl
alcohol and at least one selected from the group consisting of
starch, modified starch and a sugar. Preferably, the
hydroxy-containing polymer is a combination of polyvinyl alcohol
and starch. In the instance when the (a') PVOH is combined with
(a'') starch and/or modified starch and/or sugar, the ratio of
(a'): (a'') preferably ranges from 1:0.001 to 1:50. More
preferably, the ratio of (a'):(a'') ranges from 1:0.1 to 1:5. These
ratios are based on the weight of (a') and the weight of (a'').
[0035] The starch component may be a native or granular starch
selected from the group consisting of potatoes, rice, tapioca,
corn, peas, rye, oats, wheat and combinations thereof.
Alternatively, the starch may be a modified starch, such as a
hydrolysis product thereof (e.g. dextrin).
[0036] Surprisingly, it has been discovered that certain polyacids,
their salts and anhydrides can be dissolved in viscous aqueous PVOH
solutions, thereby decreasing their viscosity and increasing the
non-volatiles content of the aqueous compositions. In an embodiment
of the invention, the curable aqueous composition is prepared in a
concentrated form hereinafter referred to as a "concentrated
resin". The concentrated resin is diluted prior to curing, usually
at the application site where it is combined with the fibers and
then cured. Generically, both the concentrated resin form and the
diluted resin form are herein referred to as the "curable aqueous
composition".
[0037] In an embodiment of the invention, is a method for forming a
non-woven material comprising: mixing fibers with said binder, and
heating the binder and fibers at 130.degree. C. to 230.degree. C.
for sufficient time to effect cure. Preferably, the diluted resin
form comprises greater than 1% by weight of nonvolatiles
immediately prior to curing. More preferably, the diluted resin
form comprises 2 to 12% by weight of nonvolatiles immediately prior
to curing. Most preferably, the diluted resin form comprises 3 to
6% by weight of nonvolatiles immediately prior to curing.
[0038] The concentrated resin is substantially infinitely
water-dilutable, and the binder can be mixed with the nonwoven
fiber material by spraying, soaking or other suitable methods
commonly used by the industry. The material is then dried and the
binder is cured in an oven at elevated temperatures, generally at
130-250.degree. C. providing for the formation of a rigid thermoset
polymer. Initially, when the binder is applied to the nonwoven, the
binder is used in an excessive amount compared to the amount of
nonwoven. However, upon curing of the binder, the final product
preferably contains up to 10 wt % of cured polymer, more preferably
from 2 wt % to about 8 wt % of cured polymer, wherein the wt % is
based on the amount of fiber and cured polymer. It is envisioned
that the fiber surface can be pretreated prior to application of
the binder, e.g., with adhesion promoters, however, this is not
preferred in view of the cost of this step.
[0039] In an embodiment of the invention, the PVOH is chosen so as
to enable the preparation of a high-non-volatiles concentrated
resin. A higher concentration of non-volatiles is important to the
cost of its shipping and storage in view of the reduced volume of
the composition. Preferably, the PVOH has a viscosity of up to 10
centipoise in a 4 wt % aqueous solution at 20.degree. C. More
preferably, the PVOH has a viscosity of 3.8 to 10.0 cps, and even
more preferably the PVOH has a viscosity of 2.5 to 7.0 cps, and
most preferably, the PVOH has a viscosity of 2.5 to 5.0 cps.
Preferably, the PVOH has a number average molecular weight (as
measured by light scattering) of greater than 7,000. Preferably,
the number average molecular weight is in the range of 12,000 to
85,000.
[0040] Most preferably, the polyvinyl alcohol has a number average
molecular weight in the range of greater than 13,000 to 45,000.
Preferably, the PVOH has a weight average molecular weight (as
measured by light scattering) of up to 85,000. More preferably the
PVOH has a weight average molecular weight of 7,000 to 55,000, and
most preferably, the PVOH has a weight average molecular weight of
13,000 to 23,000.
[0041] The PVOH can be formed from conventional methods known in
the art and the method is not particularly restricted. It is
preferred that the PVOH is not subjected to a modification
reaction, such as free radical copolymerization with vinyl or
acrylic monomers, prior to reaction with the multifunctional
crosslinking agent (b). In an embodiment of the invention, the PVOH
is a partially hydrolyzed polyvinyl acetate, or is a copolymer of
ethenol and vinyl acetate. Fully hydrolyzed grades of PVOH, i.e.,
at least 98 mole % hydrolyzed, provide high tensile strength of the
final product. However, these fully hydrolyzed grades are
characterized by a higher viscosity of aqueous solutions.
Preferably, the PVOH is from 70 mole % to 99 mole % hydrolyzed.
More preferably, the PVOH is from 80 mole % to 90 mole %
hydrolyzed.
[0042] In an embodiment of the invention, the polyacids used as
cross-linkers for PVOH are acids having at least two acidic
functional groups that will react with the alcohol moieties on the
PVOH. It is preferred to use nonpolymeric polyacids. These
nonpolymeric polyacids include at least one of maleic acid,
succinic acid, citric acid, phthalic acid, glutaric acid, malic
acid, phthalic acid or the like, and salts thereof.
[0043] In an embodiment of the invention, the cross-linker for PVOH
is the anhydride of the nonpolymeric polyacid. These anhydrides
include at least one of maleic anhydride, succinic anhydride,
phthalic anhydride and the like. However, the use of anhydrides is
not preferred in view of the tendency for the anhydride to lower
the pH of the composition to unacceptably low levels and an extra
step of neutralizing the composition with a base is required. In an
embodiment of the invention, the PVOH is crosslinked without an
anhydride.
[0044] In an embodiment of the invention, the cross-linker for PVOH
is a nonpolymeric polyaldehyde having at least two aldehyde groups
capable of reacting with the alcohol moieties on the PVOH.
Preferably, the nonpolymeric polyaldehyde is at least one selected
from the group consisting of glyoxal or glutaraldehyde.
Polyaldehydes are effective crosslinkers of PVOH because of their
high activity. However, a disadvantage of such a high activity may
be a low stability of the PVOH-based binder and/or the reaction of
polyaldehyde with other components of the composition before the
curing. To prevent these undesirable reactions, the polyaldehyde
can be blocked by reaction with a blocking agent at most or all of
the aldehyde groups on the polyaldehyde before adding to the
composition, as it was described in U.S. Pat. Nos. 4,695,606;
4,625,029, and 4,656,296, each of which are incorporated herein by
reference in their entirety. The blocking agent inhibits the
polyaldehyde from reacting with other components prior to drying.
The inventive process can tolerate some free aldehyde (unblocked)
groups, i.e., up to about 3 wt % of free aldehyde based on the
weight of the composition, but it is preferred to have essentially
all of the aldehyde groups blocked.
[0045] Suitable blocking agents include urea, substituted ureas
(such as dimethyl urea), various cyclic ureas, carbamates (such as
isopropyl or methyl carbamate), glycols, polyols (i.e. containing
at least three hydroxy groups), unalkylated or partially alkylated
polymeric glyoxal derived glycols such as
poly(N-1',2'-dihydroxyethyl-ethylene urea) and mixtures thereof.
Preferably, the blocking agent is a urea or cyclic urea because the
blocked glyoxal resins formed are very stable providing long shelf
life.
[0046] Typical examples of cyclic ureas include, but are not
limited to, ethylene urea, propylene urea, uron,
tetrahydro-5-(2-hydroxyethyl)-1,3,5-triazin-2-one,
4,5-dihydroxy-2-imidazolidone, 4,5-dimethoxy-2-imidazolidinone,
4-methyl ethylene urea, 4-ethyl ethylene urea, 4-hydroxyethyl
ethylene urea, 4,5-dimethyl ethylene urea, 4-hydroxy-5-methyl
propylene urea, 4-methoxy-5-methyl propylene urea,
4-hydroxy-5,5-dimethyl propylene urea, 4-methoxy-5,5-dimethyl
propylene urea, tetrahydro-5-(ethyl)-1,3,5-triazin-2-one,
tetrahydro-5-(propyl)-1,3,5-triazin-2-one,
tetrahydro-5-(butyl)-1,3,5-triazin-2-one, dihydro-5-methyl-2(1H,
3H) pyrimidinone, dihydro-5,5-dimethyl-2 (1H) pyrimidinone,
tetrahydro-4-5-methyl-2 (1H) pyrimidinone,
tetrahydro-4-(2-hydroxyethyl)-5,5-dimethyl-2 (1H) pyrimidinone, and
the like, and mixtures of these.
[0047] The polyol may be any of a wide variety of materials,
including but not limited to ethylene glycol (to make
2,3-dihydroxydioxane), diethylene glycol, dialkylene glycol (to
make an oligomeric condensation product) such as 1,2-propylene
glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene
glycol, 1,4-butylene glycol, polyethylene glycols having the
formula HO(CH.sub.2CH.sub.2O).sub.nH where n is 1 to about 50, and
the like, and their mixtures. Other suitable polyols (i.e.
containing at least three hydroxy groups) can be used, such as
glycerin, (to make 2,3-dihydroxy-5-hydroxymethyl dioxane) as well
as unalkylated or partially alkylated polymeric glyoxal derived
glycols such as poly(N-1',2'-dihydroxyethyl-ethylene urea),
dextrans, glyceryl monostearate, ascorbic acid, erythrobic acid,
sorbic acid, ascorbyl palmitate, calcium ascorbate, calcium
sorbate, potassium sorbate, sodium ascorbate, sodium sorbate,
monoglycerides of edible fats or oils or edible fat-forming acids,
inositol, sodium tartrate, sodium potassium tartrate, glycerol
monocaprate, sorbose monoglyceride citrate,
.alpha.-D-methylglucoside, sorbitol, dextrose, and their
mixtures.
[0048] In an embodiment of the invention, the formaldehyde-free
curable aqueous composition of this invention may optionally
contain cure accelerators (catalysts). The catalyst according to
the present invention is selected from the group consisting of zinc
chloride, zinc nitrate, ammonium chloride, ammonium sulphate,
magnesium chloride, magnesium acetate, aluminum sulphate, aluminum
chloride, sodium hypophosphite, sodium phosphite, and mixtures
thereof.
[0049] In an embodiment of the invention, the viscosity of the
curable aqueous composition is reduced to improve its suitability
for some industrial applications. In these compositions, low
molecular weight extenders and/or viscosity modifiers are added to
improve processability of the binder. Any extender known in the art
can be used, but it is preferred that the extender is urea,
ethylene urea, or mixtures thereof, in an amount of 5 to 100 parts
based on 100 parts of PVOH. Preferably, the extender is used in an
amount of 20 to 70 parts, and most preferably, the extender is used
in an amount of 35 to 50 parts based on 100 parts of PVOH. Any
viscosity modifier known in the art that is compatible with the
curable aqueous composition can be used, but it is preferable to
use low molecular weight polyols. The low molecular weight polyol
is at least one selected from the group consisting of glucose,
sucrose, sorbitol, ethylene glycol, diethanolamine,
triethanolamine, or the like. Preferably, the viscosity modifier is
used in an amount of 35 to 80 parts based on 100 parts PVOH, and
most preferably, the viscosity modifier is used in an amount of 45
to 65 parts based on 100 parts PVOH.
[0050] In an embodiment of the invention, the curable aqueous
composition includes other components, e.g. emulsifiers,
plasticizers, anti-foaming agents, biocide additives, anti-mycotics
including, e.g., fungicides and mold inhibitors, adhesion promoting
agents, colorants, waxes, antioxidants, corrosion inhibitors and
combinations thereof.
[0051] In an embodiment of the invention, the curable aqueous
composition includes solvents other than water to promote intimate
mixing of the components.
[0052] The manner in which the PVOH is combined with the
cross-linker can affect the concentration of the non-volatiles
formed. One method of the present invention comprises a step of
preparing one solution of PVOH and one solution of cross-linker and
a second step of mixing the two solutions. However, a preferred
method of the present invention comprises a first step of forming a
PVOH solution and a second step of adding the crosslinker directly
to the PVOH solution. This preferred method is surprising since it
can have the advantage of improved viscosity while increasing the
concentration of the non-volatiles formed, e.g., it was surprising
that dissolving solid maleic anhydride allows for the simultaneous
decrease in the viscosity with the increase in solid
concentration.
[0053] In an embodiment of the invention, the curable aqueous
composition is a concentrated solution and is produced having a
non-volatiles content of greater than 25 wt %.
[0054] Preferably, the non-volatiles content is greater than 30 wt
%, and most preferably, the non-volatiles content is 32 wt % to 43
wt % based on the weight of the concentrated resin composition.
This concentrated resin composition is a clear solution.
[0055] The concentration of the curable aqueous composition to be
applied to the fiber depends on the type of fiber. In an embodiment
of the invention, the curable aqueous composition to be applied to
the fiber is produced having a non-volatiles content of at least 1%
by weight. Preferably, the non-volatiles content is 2 wt % to 12 wt
%, and most preferably, the non-volatiles content is 3 wt % to 6 wt
% based on the weight of the binder. This binder is a clear
solution.
[0056] In an embodiment of the invention, the concentrated resin
has a viscosity of below 1000 centipoise, preferably, below 750
centipoise when measured at 30 wt % aqueous solution at 20.degree.
C. As mentioned above, the concentrated resin can be stored and
shipped to an application site. Immediately before the application
to the fiber, it is diluted by water (and optionally, combined with
other additives) to form the binder. Most preferably, the
concentrated resin has a viscosity of below 500 centipoise.
[0057] In an embodiment of the invention, the cross-linking
reaction can optionally be performed with a catalyst. It is
preferred to perform the curing reaction without a catalyst. The
PVOH and the multifunctional crosslinking agent can be
self-crosslinked by heat providing the formation of a rigid
thermoset polymer. This curing reaction is performed at a
temperature between 130.degree. C. and 250.degree. C. for 3-10
minutes. Preferably, the reaction is performed at a temperature
between 130.degree. C. and 220.degree. C. for 3 to 10 minutes, and
most preferably, the reaction is performed at a temperature between
150.degree. C. and 210.degree. C. for 3 to 7 minutes.
[0058] The amount of crosslinking is related to the degree of the
cure of a curable composition and is measured herein by Retention
%. The higher the retention indicates a higher degree of
cross-linking.
[0059] The curable aqueous composition of the invention can be used
to prepare nonwoven products by a variety of methods known in the
art, which, in general, involve the impregnation of a loosely
assembled mass of fibers with the binder solution to form a mat.
The fibers may comprise natural fiber such as cellulose, wool,
jute; synthetic fibers such as polyesters, acrylics, nylon,
polyamides, ceramics, glass fibers, and the like, alone or in
combinations with one another. Preferably the product is used in
paper impregnation, building insulation, a roofing fiberglass mat
or a nonwoven filtration material.
[0060] Generally, fibers having a length of about 1/4 inch to 3
inches and a diameter of about 3 to 20 microns are used in the
wet-laid process (for example, roofing materials production).
[0061] Glass fibers typically used in manufacturing insulation
products (that are produced using melt-blown technique) range in
diameter from about 2 to 9 microns, and have a length of about 1/2
inch to 2 inches.
[0062] Herein, the number average molecular weight of the polymers
is determined by the light scattering technique. The viscosity is
determined by a Brookfield viscosimeter (#2 spindle, 30 rpm).
[0063] Herein, the term "nonpolymeric" is used to define a compound
which will not form covalent bonds with itself under the reaction
conditions for mixing the components and for the curing reaction of
the present invention and the term includes compounds which are
preliminarily formed by covalently linking up to three identical
monomers prior to curing with PVOH.
[0064] Unless otherwise indicated, all concentrations in weight
percent as described herein are based on the entire weight of the
composition.
EXAMPLES
Use of Polyaldehydes as Cross-Linkers:
Example 1 (Comparative)
Preparation of binder containing PVOH and a Polyaldehyde:
[0065] PVOH solution was prepared by adding a sufficient amount of
solid PVOH (CELVOL.RTM. 205S, by Celanese, 88.5% hydrolyzed), to
water to form a 25 wt % solution wherein the wt % is based on the
weight of the composition. 100 grams of PVOH solution were mixed
with 31 grams of 40 wt % glyoxal. The final composition had
infinite water dilutability (WD). However, it was gelled in 10
minutes at room temperature.
Example 2 (Inventive)
Preparation of Blocked Glyoxal (1)
Ethylene Urea--Ethylene Glycol--Glyoxal Condensate (EEG):
[0066] To a 1-liter 3-necked flask equipped with a mechanical
stirrer, reflux condenser, and thermometer were charged 102 grams
of ethylene urea (40 wt %), 39 grams of ethylene glycol, and 97
grams of glyoxal (40 wt %). Initial pH of the mixture was 4.3. The
mixture was stirred, heated to 70.degree. C., and held at this
temperature for four hours. The product (EEG) was a clear yellow
liquid with NV %=43.6%, pH=3.9 and infinite WD. The composition was
stable for at least 3 months (clear, no gellation, infinite
WD).
Example 3 (Inventive)
Preparation of Blocked Glyoxal (2)
Sorbitol--Glyoxal Condensate (SG):
[0067] To a 1-liter 3-necked flask equipped with a mechanical
stirrer, reflux condenser, and thermometer were charged 130 grams
of sorbitol (70 wt %) and 145 grams of glyoxal (40 wt %). The
mixture was stirred, heated to 75.degree. C., and held at this
temperature for four hours. The product (SG) was a clear colorless
liquid with NV %=54.3%, pH=2.3, and infinite WD. The composition
was stable for at least 3 months (clear, no gellation, infinite
WD).
Example 4 (Inventive)
[0068] 200 grams of 25 wt % aqueous solution of PVOH (CELVOL.RTM.
205S) were mixed at room temperature with 115 grams of EEG (Example
2), at a ratio of 1:1 (by weight per non-volatiles). The resin
composition had NV %=30.7%, pH=5.7, an infinite WD, and was stable
for at least 2 months at room temperature.
Example 5 (Inventive)
[0069] 200 grams of 25 wt % aqueous solution of PVOH (CELVOL.RTM.
205S) were mixed at room temperature with 92 grams of SG (Example
3), at a ratio of 1:1 (by weight per non-volatiles). The resin
composition had NV %=32.8%, pH=5.3, an infinite WD, and was stable
for stable for at least 2 months at room temperature.
Example 6 (Inventive)
Binder Compositions
[0070] The resins of Examples 4-5 were combined with the catalysts
to give final binder compositions. These compositions are given in
the following Table 1. TABLE-US-00001 TABLE 1 Binder Compositions
Example # Resin parts Additive* Additive parts A 4 100 -- -- B 4 95
AC 5 C 5 94 CA 6 D 5 96 AS 4 *AC--ammonium chloride, AS--ammonium
sulphate, CA--citric acid
Example 7 (Inventive)
Tensile Testing of Cured Glass Fiber Specimens
[0071] Binder Compositions A-D were each individually diluted with
water to give a binder solution having 5% non-volatiles, and the
binder solution was applied to a glass fiber substrate as
follows.
[0072] Glass paper (Whatman 934-AH) was soaked in the binder
solution for 10 minutes, then the excess liquid was removed by
vacuum. The samples were put into an oven at 200.degree. C. for 5
minutes for curing of the binder resin.
[0073] The cured samples were cut into specimens having the
dimensions of 6''.times.1'' and tested for dry tensile strength by
placing them in the jaws of a Lloyd Instruments LRX Plus tensile
tester. Samples were pulled apart at a crosshead speed of 2
inches/minute.
[0074] For wet tensile testing, the specimens were treated with hot
water at 80.degree. C. for 10 minutes, and then tested for tensile
strength while still wet. Retention was calculated as a ratio Wet
strength/Dry Strength. Retention is a measure of the degree of cure
of a curable composition: higher retention indicates higher degree
of cross-linking.
[0075] The load in Kgf was measured at the break. The test results
are presented in the Table 2. TABLE-US-00002 TABLE 2 Dry strength,
Wet strength, Retention, Binder kgf kgf % A 6.5 1.2 18 B 6.3 4.7 75
C 6.1 4.8 79 D 6.9 5.0 72
[0076] The results indicate that the cure of glyoxal-based systems
can be significantly improved upon addition of an acidic catalyst.
Binder A was cured without catalyst, and shows an insufficient
degree of cure. On the contrary, PVOH based compositions B-D cured
with an acidic additive showed high wet strength and retention.
Use of Polyacids as Cross-Linkers:
Example 8 (Comparative)
[0077] The example of the '849 patent was repeated as a comparative
example to show that the pH of the final binder solution was
outside of the present invention.
[0078] Following the instructions given for Example 1 of the '849
patent, a 30% aqueous solution was prepared using the low MW PVOH
(CELVOL.RTM. 502, Celanese) of the '849 patent which is taught at
column 5, lines 38-39 of the '849 patent to have an Mn<7,000. A
30% aqueous solution of maleic anhydride was separately prepared.
Then both solutions were combined. In this final solution, the
ratio of PVOH to maleic anhydride was 1:1, and pH was found to be
1.0.
Example 9 (Inventive)
[0079] Comparative Example 8 was essentially repeated, except that
the binder composition was neutralized with 29% ammonium hydroxide
to pH=3.5.
Example 10 (Inventive)
Testing of Cured Glass Fiber Specimens
[0080] The tensile testing for Resin Compositions of Comparative
Example and Inventive Example 9 was conducted in the same manner as
described above for Binder Compositions A-D in Example 7.
[0081] Also, the water resistance was evaluated by the time needed
to absorb a droplet of water put on surface of the cured glass
fiber sheet. The same samples were used that were tested for
tensile strength.
[0082] The results are shown in Table 3. TABLE-US-00003 TABLE 3 Dry
Wet Water Binder strength, kgf strength, kgf Retention, %
absorption, min Comparative 4.9 2.3 47 0.1 Example 8 Inventive 6.0
4.9 82 2.0 Example 9
[0083] The results indicate that the cure of polyacid based systems
can be significantly improved upon neutralization. The neutralized
composition showed improved strength and retention, as well as a
better water resistance.
Example 11 (Inventive)
[0084] To a 1-liter 3 necked flask equipped with a mechanical
stirrer, reflux condenser, and thermometer were charged 200 grams
of 25 wt % PVOH (CELVOL.RTM. 205S) solution. As this was stirred,
50 grams of solid maleic anhydride were added at room
temperature.
[0085] Then the temperature was raised to 60.degree. C. and the
composition was stirred until the anhydride dissolved. The solution
was cooled to 25.degree. C. to give a colorless clear liquid of pH
1.5. The composition was then neutralized by slow addition of 29%
ammonium hydroxide. The neutralized resin had pH=3.6, NV %=33.8%,
and viscosity 635 cps.
Example 12 (Inventive)
[0086] 33 grams of solid maleic anhydride were added at room
temperature to 200 grams of 25 wt % PVOH and dissolved as in
Example 11. After that, 17 grams of solid citric acid were added at
room temperature. The composition was stirred until citric acid was
dissolved, and then neutralized by ammonium hydroxide. The
neutralized resin had pH=3.5, NV %=33.5%, and viscosity 650
cps.
Example 13 (Inventive)
[0087] 50 grams of solid maleic anhydride were added at room
temperature to 200 grams of 25 wt % PVOH and dissolved as in
Example 11. After that, 40 grams of 50% citric acid and 29 grams of
70% glucose solution were added at room temperature. The
composition was stirred for 15 minutes, and then neutralized by
slow addition of ammonium hydroxide. The neutralized resin
composition had NV=35.8%, pH=3.6, and viscosity 480 cps.
Example 14 (Inventive)
[0088] To a 1-liter 3 necked flask equipped with a mechanical
stirrer, reflux condenser, and thermometer were charged 42 grams of
solid maleic anhydride and 63 grams water. The mixture was stirred
at 65.degree. C. until the anhydride was dissolved. In a beaker,
slurry was prepared of 42 grams starch (Water soluble starch, ACS
reagent from Sigma-Aldrich), and 63 grams water. This slurry was
slowly added to the maleic anhydride solution at a continuous
mixing. The temperature was kept in the range of 80-85.degree. C.
After all starch was added, the liquid was mixed for additional 15
minutes at 80.degree. C. After that, it was cooled down to
60.degree. C. To the mixture, 224 grams of 25 wt % PVOH, 42 grams
of solid maleic anhydride and 14 grams of solid citric acid were
added. The composition was stirred at 60.degree. C. until crystals
were dissolved, and then neutralized by slow addition of ammonium
hydroxide. The neutralized resin composition had NV=36.1%, pH=3.5,
and viscosity 385 cps.
Example 15 (Inventive)
Testing of Cured Glass Fiber Specimens
[0089] Testing for Resin Compositions of Examples 11-14 was
conducted in the same manner as described above in the Example 10.
The results are shown in Table 4. TABLE-US-00004 TABLE 4 Binder,
Dry strength, Wet strength, Water Example # kgf kgf Retention, %
absorption, min 11 6.1 4.9 80 2 12 6.2 5.8 94 48 13 6.0 5.2 87 21
14 6.6 5.1 77 60
[0090] The results indicate that the cure of polyacid based systems
can be significantly improved upon addition of citric acid in wet
strength and retention %. Binder 12 containing citric acid shows
considerably higher wet strength and retention as compared to
binder 11. The results of testing binders 13 and 14 show that good
dry strength, wet strength and retention % can be obtained upon the
addition of glucose or starch to a PVOH-based binder.
[0091] It can be seen from the results that the unmodified PVOH/MA
composition 11 shows quite a poor water resistance after cure.
However, the addition of citric acid, as well as starch and
glucose, improves the water resistance of the cured polymer,
probably because of additional cross-linking and increase in cure
density.
[0092] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *